The present invention relates generally to an automotive steering apparatus and more particularly to novel means for damping or reducing the level of noise otherwise transmitted from the front wheels or from the internal combustion engine of a vehicle to the interior thereof.
It is common knowledge that automotive vehicles are subject to noise of high frequency and low amplitude which, if allowed to penetrate into the passenger cabin, may make driving an unpleasant experience. Such noise may result from many different factors; but among its chief sources are the wheels interacting with more or less smooth road surfaces and/or the internal combustion engine. Attempts have, of course, not been lacking to seek means for breaking the chain of transmission of such noise between its source and the interior of automotive vehicles.
Thus it is conventional in steering mechanisms to provide tie rods for connecting the steering arms associated with the front wheels to the motion transmitting member of a steering gear mechanism comprising a bracket to which both tie rods may be connected and a moving member, and to provide elastic means between the bracket and the moving member.
West German patent specification DE-PS No. 767,117, for instance, discloses a rack and pinion steering mechanism in which the tie rods are connected to a forward portion of a toothed rack which functions as the moving member. Elastic means or rubber blocks are provided between each tie rod and the rack. During a steering operation these elastic means may be subjected to compression; but for purposes of maintaining a rigid connection between the tie rods, the intermediate elastic means notwithstanding, there is provided a rod which extends through the rack in a loosely guided manner to which joint portions of the tie rod joints are connected.
This arrangement is intended to dampen shocks generated by the front wheels, without adversely effecting their substantially parallel alignment. However, since in a steering operation steering force is transmitted by the elastic blocks, the blocks need to be made of relatively stiff material in order to avoid excessive lost motion or free play. This, however, may lead to the transmission of noise and/or vibrations of high frequency and low amplitude generated by the road surface and/or the engine into the interior of the vehicle, from the wheels and possibly the drive shafts to the steering mechanism by way of the tie rods and from the steering gear by way of the steering column. Also, the loosely guided rod in the rack constitutes a strong noise transmitter.
It is also well known elastically to mount the steering gear unit to the chassis or frame of automotive vehicles. Such elastic mounting may, however, result in undesirable movements of the steering gear unit during steering operations, i.e. when steering force is applied or transmitted. Also, such mounting cannot prevent the transmission of noise to the interior of the vehicle.
It is, therefore, an object of the invention to provide for an improved steering apparatus of the kind referred to which by simple means eliminates or at least substantially reduces the transmission of high frequency body vibrations.
Another object of the invention resides in the provision of novel means for reducing the level of transmission of high frequency body noise from the tie rods of an automotive steering mechanism to the steering gear.
A further object of the invention is to provide a novel high frequency noise damping arrangement in an automotive steering apparatus.
Yet another object of the invention resides in providing elastic means between tie rods and steering gear of an automotive vehicle which when subjected to thrust or compression transmit insignificant steering forces only.
A still further object of the invention is to provide an elastic connection between tie rods and motion transmitting device of a steering gear with a predetermined lost motion or free play.